The invention relates to a locking mechanism for a belt retractor comprising an inertia element supported in a bearing to be rotatable between a home position and a locked position.
A belt retractor is used to protect a vehicle occupant by means of a seat belt. The seat belt is wound onto a belt reel from which it can be extended. In the case of need, for example with extreme vehicle deceleration, the belt reel is blocked to be rotationally fixed in the unwinding direction of the seat belt so that no further seat belt can be extended. Hence a vehicle occupant buckled with the seat belt takes part in the vehicle deceleration. For blocking the belt reel, the belt reel can have a toothing which does not obstruct rotation of the belt reel during normal operation. In the case of need, the belt reel is transferred to a blocking position in which the toothing of the belt reel engages in one or more recesses at the frame of the belt retractor. In the blocking position the belt reel is thus retained to be rotationally fixed against rotation in the unwinding direction of the seat belt.
For transferring the belt reel from the idle position into the blocking position the locking mechanism is used. The locking mechanism usually includes an inertia element which during normal operation can follow the rotation of the belt reel. In a home position the inertia element is biased by means of a spring in the direction of rotation and is pivoted to a bearing point so that, in the case of need, by a faster webbing extension due to the forward displacement of the occupant with great vehicle decelerations the inertia element is deflected, due to its inertia, about the bearing point into a locked position. The inertia element includes a ratchet which is inserted into the toothing of the belt retractor frame by the afore-described process in the case of need. In order to realize the pivoting motion of the inertia element, the latter is typically arranged on a cylindrical bearing point of the reel.
The drawback with this support of the inertia element is that the contact point between the bearing point and the inertia element migrates depending on the rotary position of the belt reel, as tolerances are provided between the inertia element and the bearing point. This migration of the contact point is due to gravity, as the belt reel, and related thereto the contact point between the bearing point and the inertia element, is vertically arranged. Depending on the rotary position, the contact point thus migrates depending on the position of the inertia element relative to the entire belt reel. At a “6 o'clock” position the inertia element is provided, for example, in the lower area of the belt reel, and the contact point of the inertia element at the bearing point is provided at a side facing the central axis of the belt reel. When the belt reel is rotated about 180° during normal operation, the inertia element is provided at a “12 o'clock” position, i.e. in the upper area of the belt reel. The contact point between the inertia element and the bearing point is then located on a side facing away from the central axis of the belt reel, because due to gravity the inertia element “rests” on the bearing point. By reason of this migration of the contact point, the position of the inertia element relative to the belt reel will influence the insertion of the belt reel. Moreover, friction occur by reason of the migration of the contact point, thereby the components being subjected to wear.